This invention relates to the transmission of signals on a multi-phase (3φ) power transmission system using a two-way communications system (TWACS®), and more particularly to the concurrent transmission of data and other information on more than one of the phases.
It is known to transmit and receive messages on an electrical distribution system. Patents teaching a two-way communications system and the techniques employed in two-way communication include U.S. Pat. Nos. 5,696,441, 5,486,805, 5,262,755, 4,996,513, 4,963,853, 4,918,422, 4,914,418, and 4,658,238 all of which are assigned to the same assignee of the present application. In practice, a request for information or data is formulated into an “outbound” message that is injected into one phase of a three-phase power distribution network and transmitted through the network to a remote location such as an electrical meter on a building. The message may, for example, request information such as to the current electrical consumption at the site. A reply, or “inbound” message is then transmitted back over the same phase to the transmission site, which is typically a substation in the power grid comprising the distribution system. When the inbound message is processed, the requested information is then used to measure such things as total demand on the system at that particular time.
TWACS is used in conjunction with various remote devices such as automatic metering reading (AMR) equipment, load control devices and other types of monitoring and control equipment installed throughout the distribution system in homes, factories, office buildings, etc. After installation, each remote device can be accessed through one of six communication paths. A communication path consists of the outbound phase combination of phasor, AN, BN, CN, AB, BC or CA and the inbound return path φA, φB, or φC. The communication path is defined by the electrical connection for each location. After installation, the communications path is determined by the system and recorded for later use. Accordingly, when a series of remote devices, such as meters are in place, some will return an inbound signal on φA, but not a signal on φB or φC; other remote devices will return an inbound signal on φB, but not a signal on φA or φC; and, some remote devices will return an inbound signal on φC, but not a signal on φA or φB.
In the current system, after an outbound message is issued on one phrase combination and while the inbound response is being returned, no other outbound and inbound processing can occur until the inbound processing is completed. The problem this presents is the delay in the transmission and reception of outbound and inbound TWACS signals, and the consequent limiting of the amount of information, which can be sent and received through the system at any one time. If it were possible to be able to concurrently send and receive signals on all three phases, the bandwidth of the communications network would be effectively tripled improving information flow and system response time.